1. Field of the Invention
This invention generally relates to the quality of flat glass produced by the float process and, more particularly, to a cleaning apparatus for removing uneven and crusty deposits from the surfaces of conveying rolls employed in such process.
2. Description of the Prior Art
A conventional float apparatus for producing float glass is illustrated and described in U.S. Pat. No. 3,083,551, issued on Apr. 2, 1963. As there explained, the float process involves the delivery of molten glass at a controlled rate onto a bath of molten metal such as tin or an alloy of tin, and advancement thereof along the surface of the bath under thermal and mechanical conditions which assure that (1) a layer of molten glass will be established on the molten metal bath, (2) from this molten glass layer there will develop on the surface of the metal bath a buoyant body of molten glass of stable thickness, and (3) as this glass body of stable thickness develops, it is continually advanced in ribbon form, along the bath and sufficiently cooled to permit its being taken from the bath at the exit end thereof by lift-out conveyor rolls. The newly formed ribbon of glass is then advanced through an annealing lehr on driven conveyor rolls which provide the tractive force to draw the glass ribbon along the metal bath. The glass ribbon is at an elevated temperature as it leaves the exit end of the metal bath and enters the entrance end of the annealing lehr and, accordingly, it is in a soft or plastic condition.
Glass produced by the above-described process is of high quality and is said to have fire-polished surfaces. However, because the newly formed glass ribbon is in a plastic condition as it leaves the metal bath and enters the annealing lehr, it is subject to a defect known in the art as "roll print". Roll print, characterized by broad band distortion such as random surface rub marks, fissures, and in some cases even fractures, is caused by the mechanical contact of the glass ribbon with lift-out and lehr conveyor rolls which have uneven and crusty deposits on their surfaces which imprint on the soft undersurface of the newly formed glass ribbon.
In the case of the lift-out rolls, the uneven and crusty deposits are thought to be formed on the surfaces thereof by (1) the carryover of dross adhering on the glass ribbon from the molten bath which is deposited on the rolls, (2) vapors from the bath which condense and deposit on the rolls and, (3) carbon deposits which adhere to the rolls from the elongated carbon blades of the sealing means conventionally employed to seal the exit end of the float chamber from the surrounding atmosphere.
In the case of the lehr conveyor rolls, especially these rolls adjacent the lehr entrance, the uneven and crusty deposits are thought to be formed on the surfaces thereof by the carryover of tin enriched vapors which condense and deposit themselves on the rolls as a crusty layer of non-uniform thickness as well as the carryover of dross and other foreign matter adhering on the soft undersurface of the glass ribbon.
Attempts have been made in the past to remove impacted crusty deposits from the surfaces of such conveyor rolls in situ. For example, U.S. Pat. No. 3,337,320, issued on Aug. 22, 1967, teaches a method of removing deposits from the surfaces of lehr rolls by steam and U.S. Pat. No. 3,481,727, issued on Dec. 2, 1969, teaches the use of a reciprocating abrasive tool for abrading and brushing the crusty deposits from the surfaces of conveyor rolls. However, the methods and devices disclosed in these patents have not been entirely satisfactory in that the steam device will not remove heavily impacted crusty deposits from the roll surfaces and the abrading device may damage the roll surface itself. Also, the abrading device is subject to the disadvantage that the abrasive blocks employed load up with the hard crusty debris and thus tend to scratch the polished surfaces of the conveyor rolls which may cause even more roll imprint to occur on the newly formed glass ribbon.